As a conventional copying machine, composite apparatus having both copying and facsimile functions, or image scanner having an automatic document feeder (ADF), there has been proposed an apparatus having both a function of scanning a document fixed on a glass surface and a function of scanning a document by moving the document (feed reading).
For example, in an image reading section shown in FIG. 14, a contact type image sensor (CIS) 1 serving as an image reading device is arranged below platen glass 2. This arrangement makes it possible to perform a method of reading a stationary document D placed on the platen glass 2 while the CIS 1 is kept moving along the subscanning direction and a method of reading a document D fed along the CIS 1 kept stopped at the position of second glass 2a. 
The arrangement of a conventional contact type image sensor will be described below. FIG. 15A is a perspective view showing the arrangement of the conventional contact type image sensor 1. FIG. 15B is a sectional view of the contact type image sensor 1. The contact type image sensor 1 shown in FIG. 15A has an LED array 4 serving as a light source made up of a plurality of arrayed LEDs 3. The pair of LED arrays 4 are disposed on the two sides of a cylindrical rod lens array 5. A one-dimensional light-receiving element array 6 is disposed below the cylindrical rod lens array 5. These members are laid out in a frame 7. Cover glass 8 is attached to the upper portion of the image sensor 1.
Light emitted from the LEDs 3 irradiates the stationary document D placed on the platen glass 2, as shown in FIG. 15B. Light reflected by the document D is focused on the one-dimensional light-receiving element array 6 such as a CCD through the cylindrical rod lens array 5.
FIG. 16A is a perspective view showing the arrangement of another conventional contact type image sensor. As shown in FIG. 16A, this image sensor includes an LED 3 serving as light guide source and a light guide 11 for guiding light from the LED 3 to a document. The LED 3 is fixed on one of the longitudinal end portions of the light guide 11 (one LED at the left end in the illustrated example). Light emitted from the LED 3 is repeatedly reflected and propagates in the light guide 11 and emerges along the entire length of the light guide 4.
The light emerging from the light guide 11 irradiates the stationary document D placed on the platen glass 2, as shown in FIG. 16B. The light is then focused on a one-dimensional light-receiving element array 6 such as a CCD through a cylindrical rod lens array 5. These image sensor constituent members are laid out in a frame 7.
A conventional image sensor reciprocates in directions indicated by a double-headed arrow A as shown in FIG. 14. The image sensor is moved to the end portion of the image reading section, as indicated by a dotted line at the reading range end position. As shown in FIG. 17, a frame 9 for supporting the platen glass 2 is disposed at this end portion. When the image sensor 1 further moves, it collides with the frame 9. In order to prevent this collision according to the conventional case, the reading range end position is inevitably set before this collision position. This results in a large apparatus and particularly a large image reading section.
In the conventional image sensors like the ones shown in FIGS. 15B and 16B, when a document is irradiated from the lower side, and reflected light is incident on the one-dimensional light-receiving array 6 through the cylindrical rod lens array 5, light preferably irradiates the document placed on the platen glass 2 such that the light amount of the irradiation light beam has a peak for the document D. When the document floats from the platen glass 2, the position of the document is shifted from the light amount peak position. This makes it difficult to assure a sufficient light amount. In addition, unevenness occurs in the read image due to variations in light amount.
In the conventional image sensor shown in FIG. 16A, the LED 3 is formed at only one end of the light guide 11. In this case, a uniform light amount distribution within the illumination range is difficult to obtain, resulting in a nonuniform intensity. Generally, the farther the distance from the LED 3 increases, the smaller the light amount in the light amount distribution, as shown in FIG. 18. Since the LED 3 is arranged on only one side of the light guide 11, the absolute light amount is short to result in a decrease in scanning speed. In addition, nonuniformity in light amount distribution occurs to make it difficult to obtain an excellent image. For example, when a photograph or the like is adhered to a document and its image is to be read, the document is irradiated from one side opposite to the illumination direction, and a linear shadow or the like appears along the edge of the photograph in the read image.
As for the image sensor shown in FIG. 15A, it uses a large number of LEDs 3 to result in high cost. Further, it is difficult to obtain an excellent image due to variations in light amounts of the respective LEDs 3. In order to prevent color irregularity in reading operation, only a monochrome light source can be used.